The present invention relates to a system for enhancing the flight performance of an aircraft and, more particularly, to such a system that enhances the pitch axis maneuverability of the aircraft, as well as alleviates gust induced normal acceleration.
In recent years aircraft have been equiped with automatic flight control devices to assist the pilot's control of the aircraft. Such devices include computer assisted closed-loop maneuver enhancement systems and gust alleviation systems, such as shown in U.S. Pat. Nos. 3,841,912 and 2,745,613.
These previous systems have not been able to adequately solve a particular problem of using adversely coupled control surfaces. What is meant by this is that a horizontal stabilizer or stabilon causes a change of pitch of an aircraft in flight. Yet often times, the use of another control surface, such as a trailing edge flap, causes a change in lift as well as a downward change in pitch. Using the stabilon and a variable camber wing together requires careful coordination because of the effective coupling between the trailing edge flap and the stabilon. Significant adverse lift is generated by the stabilon and the trailing edge flap that has a destabilizing effect on pitching movement. Further, the lift generated by the trailing edge is significantly reduced by the stabilon. If the trailing edge is used to produce a significant improvement in the normal acceleration (Nz) response, it needs to be carefully balanced with the stabilon's use. Otherwise, if the stabilon is used improperly to counteract the adverse pitching movement of the trailing edge flap, the aircraft will become highly unstable.
One prior art device to provide gust alleviation that uses two control surfaces is described in U.S. Pat. Nos. 3,215,374 and 3,240,447. The systems described are for use primarily with a canard equiped aircraft and utilizes a computer to read the normal acceleration, angular rate of pitch change, and control surfaces position to generate a signal representative of the angle-of-attack increment caused by a gust. Then, the control surfaces are adjusted to counteract the normal accelaration due to the gust. A problem with the above described system is that it is really only capable of gust alleviation. Certain aircraft are now equiped with variable camber wings, i.e. wings with trailing edge and/or leading edge flaps, which need to be coordinated with the stabilon for maneuver enchancment. Nowhere is it disclosed or suggested in the two patents mentioned above to provide a system that provides both maneuver enhancement and gust alleviation. Further, the inventors hereof know of no other system that generates a signal representative of the optimum normal acceleration of the aircraft continuously while in flight and then always tries to match the actual normal acceleration with the synthesized optimum signal.